Before him, you had to the era of Japanese going straight to America which was the only way to really get quality content. But with him they didn't really need to go so far.Magnum is extremely good at making women comfortable. There is a reason he's always the first scene of a actresses interracial debut. Look at Yume Kana. Her first scene with Magnum is substantially better than the scene with a different guy. Women seem to thoroughly enjoy him. I've seen women quiver and shake but still kiss and embrace him. Its less often the case with other black performers. I can't help but think that most women having sex with him forget that they're supposed to be acting, I'm not saying its always the case but they frequently just look like they're having the best time. My personal favorite debut is Urara Kanon (not to be confused with Lala Kudou). WAAA-185, I literally have the code memorized which is rare for me. Watch it and you'll see what I'm talking about.
If he's retiring, then the golden age of interatial has ended. He carried the entire thing singlehandedly IMO. He was in every video and I never got sick of him.
There are an actual number of girls who came back numerous times specifically for scenes with magnum but also became more open to idea of interracial in general. Marina shiraishi and maria nagai called him out expressly iirc.